How I can change my bank A/C details in Paypal?

First login to your account.Go to payment Method left hand side on screen ,there is square box with + sign and link a bonk account click on then

It usually takes 3-5 business days for money from your bank account to be added to your PayPal account. Once this process is completed, money will appear in your PayPal balance and you'll be able to make online purchases or send money to anyone. Here’s how to find out when the money should arrive in your PayPal account

Good Day Pankaj S.,
you can always call the support desk at Paypal for help.

Thanks Huynh.......................